We have been seeing Google test AdSense in iPhone apps for a few months now, but not it is official. Google announced the beta for AdSense for Mobile Apps. That means that some app developers can add Google AdSense ads to their iPhone or Android applications. To apply as a developer, go here - personally, I want in!
Here are sample ads taken from Shazam on my iPhone:
Google Ad in AdSense:
Bing Ad in AdSense:
AdMob hasn't worked out great for me, but I honestly should give it another try. But I am excited to give Google AdSense for Apps a try.
Forum discussion at Google AdSense Help.